Room acoustics

Oh, @willemj  , we can't post pics directly in a thread on this forum. You'll have to post pics on your systems page or on any image hosting site, then put links in your posts on this thread. Not optimal, but..

I've actually just started using REW and was pleasantly surprised at the measurements. I do need to tame my frequencies below 200Hz, but there don't seem to be any consistent peaks now that I've brought my orange tree in the room for the winter. The very large pot of moist soil seems to have done a beautiful job as a bass absorber. Before that, I had a few peaks that wouldn't decay..
My question is this: how do I know where to put bass traps when I make them? My guess is to generate bass tones at the problem frequencies, then walk around with an SPL meter looking for areas with the highest measurements. I'd love other ideas..

And I completely agree, great thread. It seems this is more technical than most want to deal with around here, since it involves more than purchasing an item and installing it.. but we do have many members who like to dig in and who are incredibly knowledgeable, so hopefully this thread will bring that knowledge out.

Have fun! 

I have a basement listening room with low ceilings.. two things I've done that have helped reduce peaks, resonance and echos: suspended ceiling with Armstrong tiles and fully carpeted. I'll check which model of ceiling tiles I have, they weren't cheap but they do a great job of sound absorption in the mid to high frequencies

Hmm, your ears can tell you a lot, but sometimes there are some specific issues that are audible but not easily remedied. These peaks and nulls, which seem to be persistent once the easy room treatments are done, are so specific in their frequency band, that I think you'd be hard pressed to identify and fix them by ear. At least that's my experience. A little bit of data can be useful.
But your mind is still the ultimate decision maker on sonic performance. So it does have to sound good, whatever it measures

I agree it regards to treating the room, not the signal. But I'd imagine both are valid solutions with their own particular compromises. 

The waterfall graph is exactly what I've been looking at.. a very useful data visualization. What is considered an acceptable decay time for bass? I've also discovered a dip at 2k.. hmm

I’ve yet to build one, but for bass absorption, the limp membrane trap seems ideal. A member on here also recommended it to me, without me having mentioned that's what I was considering.

https://www.gearslutz.com/board/bass-traps-acoustic-panels-foam-etc/743040-tims-limp-mass-bass-absor...

All right y'all, I've posted some interesting waterfall plots on my systems page.  Check them out.  There are three measurements:
: The first is my room without any extra bass treatment, other than the bass panels behind my speakers and the acoustic panel stuck in the corner.  You can see the bass is a mess and there is a nasty frequency around 120 that lasts forever.  That would be the one-note bass i've started noticing.
: The second is with a big, potted orange tree in the corner behind and to the left of my left speaker.  There is a three panel glass sliding door on the left wall. You can see the bass is much cleaner, the bass that didn't want to die is now dead and the whole graph is much cleaner.
: The third is with a quick limp membrane bass trap I whipped up last night.  I used some dynamat i had from a car install to cover the top of a 5 gallon bucket, with a blanket thrown in to stop it all rattling on the tile floor. As you can see, it's not as clean as the orange tree, but the one note bass isn't there either.  The midrange region is definitely a bit dirtier than with the orange tree, but it's better overall than having no extra bass treatment. 

The orange tree is, oddly, the best sound treatment for my current issues. Ha! The problem is that it is sitting outside right now so it gets more sunlight so the oranges can ripen and in the summer it's outside all the time.  This means I'll need something that can either be a permanent part of the room or that i can move in when i move the tree out.  I thought I was just dealing with bass decay problems, but it looks like that corner gets a lot of midrange reverb, probably from the large amount of glass right there.  Curtains aren't an option. We have a clean look and blinds would make it feel cluttered and small, a problem in a basement with 7 foot suspended ceilings..

What I find particularly interesting are all the frequencies below 20 Hz.. I start my sweep at 20, so where is everything what coming from?

*where is everything there...

@robd2 (why don't these @things work?)

I'll generate that graph when I'm back from the dentist.

graph generated.  it's at the bottom of my system page

Thanks! That's what I was lacking.. measurements to aim for.

I'm not sure why mine is difficult to interpret and yours is easier.. I'm new to all this. I just really learned last month what a waterfall plot shows and am just now figuring out how to read it with regards to looking for problems. 

I'll try to make sense of what you just said.. I know rt60 is classified as a measure of clarity in REW, other than that, I'm in the dark. I have lots of reading to do it seems.. I'm certainly not expecting any of you to explain it to me, so I appreciate all comments. The give me things to learn and figure out.

Sweet Lord, that post will take a while to decipher. Thanks!

I just wanted to post back that my first limp membrane absorber is a smashing success. It's very deep (14") but only 10" wide and 16" tall. It's like a good size monitor speaker cabinet. I used thick vinyl for hot tub covers and used polyurethane caulk to glue two layers together, as an increase in membrane density helps to lower the effective frequencies the absorber works on.

I'll post graphs later, as I'm about to head out to dinner, but, subjectively, my 3 note bass problem is, if not gone, greatly reduced. Objectively, I have almost all bass frequencies dropping below 40db by 300ms. 

This is good fun. Sorry I seem to be the only one posting questions on this thread. I definitely appreciate your input, @s

Sorry, @shadorne